Under normal circumstances, the fund will invest at least 80% of its assets in, or derive at least 80% of its income from, securities that are exempt from regular federal income tax. The fund invests at least 60% of its portfolio in debt securities rated BBB+ or below or Baa1 or below by Nationally Recognized Statistical Rating Organizations designated by the fund"s investment adviser, or unrated but determined by the fund"s investment adviser to be of equivalent quality.